The invention is concerned with an apparatus for adjusting of cam actuated brakes through a worm gear, which is arranged in a casing defined by an actuating lever, and adjusts the camshaft of brakes from an initial position to accommodate wear of the brake linings.
Known automatic adjusters contain a worm gearing and a one-way drive mechanism which together with a linkage converts over a predetermined running clearance the angular rotation of a lever which occurs when the normal clearance between the brake drum and lining increases beyond a preset limit into a rotary motion of the wormshaft, to restore the original clearance. Until now the most commonly used one-way drive mechanisms include on helically wound coil springs either located in two consecutive sleeves as described in the U.S. Pat. No. 3,351,163, or in wrapped relationship to two interior cylindrical consecutive shafts, as described in the U.S. Pat. No. 3,507,369. In both systems, in one rotational direction the spring sticks against the above mentioned adjacent cylindrical pieces and ensures the transmission of an adjusting torque to the wormshaft, and in the other rotational direction the spring releases partially the frictional engagement and allows a relative over-running movement between the two adjacent cylindrical pieces.
In order to avoid an excessive adjustment of the brake shoe relative to the brake drum which may occur with the application of great braking force both systems limit the adjusting force either by declutching the wormshaft as in the U.S. Pat. No. 3,351,163, or by allowing slippage as in the U.S. Pat. No. 3,507,369.
The limitations of the system described in the U.S. Pat. No. 3,351,163 are reduced dependability due to the small section of the coil spring of the clutch mechanism, and therefore an expensive construction to reduce internal friction.
The limitation of the system described in the U.S. Pat. No. 3,507,369 is the difficulty in establishing the torque value at which the coil spring will allow slippage.
An other limitation common to both mechanisms consists in that the frictional contact at the beginning of the clutching does not occur precisely because of the scattering of frictional contact.